1. Field of the Invention
This invention relates to a tubular packing to be interposed between members in sliding contact with each other, and also relates to a method of producing this tubular packing.
2. Related Art
JP-A-60-84477 (prior art technique 1) discloses a sliding member such as a packing, which is produced by the steps of placing both of a band-like matrix and a band-like, sliding face-forming member one upon the other (that is, stacked together), and compressing and deforming them so that metal wires are partially exposed to the surface of the sliding member. The tubular matrix is formed by superposing a wire net of a thin stainless steel wire on a heat-resistant sheet material made, for example, of exfoliated graphite, and then by curling these members into a roll-like configuration, and then by crushing and flattening this rolled shaped members into a band-like configuration. The sliding face-forming member is formed by the steps of placing a powdered solid lubricant such as asbestos on an exfoliated graphite sheet, overlaying them with a composite net (formed by weaving or knitting a thin metal wire and a fluororesin thread together), and crushing and flattening them into a band-like configuration. Then, the two members thus produced are stacked together, and are compressed and shaped into the tubular packing. Therefore, this sliding member has the sliding surface in which the fluororesin, the thin metal wire and the solid lubricant are present in a co-existing manner, and therefore this sliding member exhibits excellent sliding properties over a long period of time.
A tubular packing, disclosed in JP-A-1-307591 (prior art technique 2), is formed by superposing one wire net (expanded metal) on one sheet of exfoliated graphite, and then by curling these into a roll-like configuration, and then by compressing (in a direction of the thickness thereof) and shaping this into a final shape of the tubular packing. Therefore, the tubular packing can be easily produced, and is less susceptible to damage.
In both of the sheet materials (tubular packings) of prior art techniques 1 and 2, the wire net and the exfoliated graphite sheet are stacked together, and then are curled into a roll-like configuration. Therefore, each of the resultant sheet materials has an increased thickness, and there has been a limit to the formation of these sheet materials into a reduced thickness. Besides, the structure of these sheet materials is complicated, and their cost is high.
There is already known a sliding sheet material of the type in which one wire net is superposed on one exfoliated graphite sheet, and then these are compressed in a direction of the thickness thereof, so that the wire net is embedded in the exfoliated graphite sheet, with the exfoliated graphite filled in the meshes (interstices) in the wire net. In this sliding sheet material, the wire net is covered with the exfoliated graphite, and the wire net is not exposed to the surface of the sliding sheet material. A tubular packing can be formed by cutting this sliding sheet material into a predetermined shape, and then by curving or bending this sheet, and then by shaping this sheet into a tubular shape of the packing.
In this tubular packing, when the exfoliated graphite sheet is worn into a reduced thickness, this causes a backlash. Besides, when the exfoliated graphite sheet is worn to such an extent that the wire net is exposed to inner and outer peripheral surfaces of the packing, the exfoliated graphite sheet comes to be severed for each mesh of the wire net, which results in a problem that the exfoliated graphite sheet is liable to separation. Furthermore, opposite end edges of the curved sheet material are not continuous with each other when the tubular packing is formed by use of the sheet, and therefore when a twisting force acts on the tubular packing, there occurs such a fear as this tubular packing is easily twisted and deformed.